Can you give a little more detail on how to utilize this? I'm having a hard time envisioning it. Thanks

Remove the valve, and spear, from the keg. Slip the 90 degree segment from the 'T' into the hole that's where the valve went. Rest the grinder against either end of the 'T' so that the blade is away from you. Turn on tool and rotate around, letting the T (a fixed rotation point) guiding your circle.

I usually mark a line with a sharpie on the keg top before cutting. That way I have something to follow along with.

Thanks for the reply. I was trying to envision something secured to the grinder but a fixed rotation point makes sense. You could even slip on varying lengths of pvc to adjust the cut. This is super simple and cheap. I like it!